With the rapid development of the display technology, the technology of semiconductor components, which is a core of the display apparatus, has experienced a great progress. For a known display apparatus composed of Organic Light Emitting Diode (OLED) devices (referred to as the OLED display apparatus briefly thereafter), which is characterized by its features such as self-illumination, fast response, wide viewing angle, and capable of being fabricated on a flexible substrate and so on, it is increasingly applied in the field of high performance display.
Because a control unit in the general OLED display apparatus includes transistors, threshold voltages Vth of the transistors are different among the different pixel units, and the Vth in the same pixel may drift over time, which may cause difference in the display brightness. Therefore, a method of compensating the threshold voltage Vth is usually used to make currents flowing through the OLED devices to be identical with each other. However, there are also some differences in a light emitting efficiency of the OLED devices in the different pixel units, such that it also can not solve completely a problem of the non-uniform brightness in the light emitted from the respective pixel units even if the currents that drive the OLED devices are the same.